The field relates to a vehicle equipped with a two-stroke cycle, opposed-piston engine. Specifically the field includes placement of a vertically-disposed, multi-cylinder opposed-piston engine in a vehicle structure, particularly that of a heavy-duty truck.
A two-stroke cycle engine is an internal combustion engine that completes a power cycle with a single complete rotation of a crankshaft and two strokes of a piston connected to the crankshaft. One example of a two-stroke cycle engine is an opposed-piston engine in which a pair of pistons is disposed in opposition in the bore of a cylinder for reciprocal sliding motion therein. Each cylinder has exhaust and intake ports. Each port is constituted of one or more arrays or sequences of openings disposed circumferentially in the cylinder wall near a respective end of the cylinder. The reciprocal movements of the pistons control the operations of the ports.
Opposed-piston engines possess a number of desirable features with respect to other two-stroke engines. Such advantages include low combustion chamber surface to volume ratio, superior scavenging, good engine balance in multiple cylinder designs, and superior power/weight ratios. These and other advantages have motivated development of vehicle designs that fit opposed-piston engines into heavy-duty trucks.
A truck is a vehicle equipped with an engine, which is designed for carrying and/or pulling loads. Medium- and heavy-duty trucks and work trucks (collectively, “heavy-duty trucks”) are usually defined in terms of weight, capacity, and/or purpose. One useful definition, which is not intended to be limiting, is found in 49 U.S.C. 32901(a)(7) and (19). Typical heavy-duty truck constructions share some common structural characteristics. Presuming placement of an engine in the front of the vehicle (“front-end placement”), radiators and other heat exchangers are located at the front of the truck's engine compartment. A single solid front axle is used with a leaf spring suspension. Solid rear axles are used, often in tandem, to drive the vehicle. The power train is oriented along the vehicle's longitudinal axis, with the transmission mounted behind the engine and a drive shaft transmitting power to the rear axle(s). The major structural elements of a heavy-duty truck include twin frame rails that run from front to rear, just inside of the wheels.
The structure of a heavy-duty truck with front-end placement can include provision for mounting the engine directly over the front axle, between the frame rails. This is typical of L-4, L-5, L-6, V-6, and V-8 engine constructions. Trucks of this type are often available with different axle setbacks, but it is still frequently the case that the engine is mounted over the front axle. Two typical cab constructions are used for front-end placement in heavy-duty trucks. One is the cab-over arrangement, where the driver's cab is mounted above the engine. In another arrangement the cab is mounted behind the engine with a bonnet (hood) to cover the engine. However, it is the case that the elongated cylinder profiles of opposed-piston engines impose unusual engine shapes which are difficult to place in these kinds of heavy-duty truck structures; nevertheless, some attempts have been made.
Commer trucks were equipped with a front-end mounted Rootes-Lister TS two-stroke, opposed-piston diesel engine situated in a cab-over construction. The engine included a row of three cylinders disposed horizontally above the truck's drivetrain. Pistons were coupled by rocker arm linkages to a single crankshaft. The TS engine was originally designed for relatively low-power applications. As power requirements increased, larger cylinders were required. However, cylinder lengths were constrained by the spacing between the truck's side rails. Thus, the horizontal orientation of the cylinders inherently limited the power levels achievable by these engines when fitted into a standard heavy-duty truck chassis. Moreover, the rocker arm linkage arrangement necessitated by the single crankshaft architecture increased the amount of engine power lost to friction, thereby limiting the efficiency achievable by the TS engine.
The problems of orientation and construction that accompany the TS opposed-engine design have placed a limit on the benefits gained by use of opposed-piston engines in heavy-duty trucks.
It is therefore desirable to enable a vehicle such as a heavy-duty truck to be fitted with an efficient, large-displacement opposed-piston engine while retaining structural characteristics common to such vehicles.